As described in co-pending U.S. patent application Ser. No. 10/629,659 entitled “Dual Polarization Vivaldi Notch/Meander Line Loaded Antenna” by John T. Apostolos, filed on Jul. 29, 2003, and as described in patent application Ser. No. 10/629,454, entitled “Combined Ultra Wideband Vivaldi Notch/Meander Line Loaded Antenna” by John T. Apostolos, filed on Jul. 29, 2003, both assigned to the assignee hereof and incorporated herein by reference, it is possible to provide an antenna element which is the combination of a Vivaldi notch and a meander line loaded antenna (MLA). These antennas in general have a top horizontal plate surrounded on two sides by downwardly depending plates which form side plates. The side plates are coupled to the horizontal plate through meander lines.
In each of these configurations there is a gap between the horizontal and vertically adjacent plates which not only requires special mounting hardware but also presents a slot.
By way of background, the purpose of providing such a combined Vivaldi notch antenna and meander line loaded antenna, is to take advantage of the high upper frequency cut-off of the Vivaldi notch antenna while establishing a minimized low frequency cut-off by utilizing the meander line loaded antenna configuration. As described in the above patent applications, the operation of these antennas provides continuous grating lobe-free coverage of, for instance, between 50 MHz and 1.5 GHz in a smooth transition between the high frequency cut-off and the low frequency cut-off. Moreover, the Vivaldi notch antennas are provided with a cavity which results in an end-fire configuration. It has been found that antennas combined in this manner produce a single lobe, and are of such a small size that they prevent grating lobes when the antenna elements are arrayed.
Moreover, when the Vivaldi notch, cavity, back facing slot structure is duplicated in the side plates and a bottom plate to provide a square horn like structure, the antenna can be operated with a number of different switchable polarities, depending on which feed points are used. As a result, with an arrangement of a horn having a top plate, two side plates, and a bottom plate, and feed points at four locations, respectively at the throats of each of the Vivaldi notches, it is possible to provide a horizontal polarization, a vertical polarization, a right hand circular polarization, or a left hand circular polarization. Assuming that the feed points in such a structure are labeled A, B, C, and D, then the following mode table specifies how the various polarizations are established:
VpolHpolRHCpolLHCpolA1011B01−i+iC1011D01−i+i
The result of the inventions in the aforementioned two patent applications is that one can establish an ultra wideband antenna having a single lobe with switchable polarizations.
While the above configurations have a relatively low low frequency cut-off, one needs the opportunity to further decrease the low frequency cut-off down to for instance 20 MHz, so as to provide a super ultra wideband antenna whose operating frequency range goes from 20 MHz to 1.5 GHz and beyond when one can ignore grating lobes.
Such an antenna would be useful in ultra wideband communications and not only for currently authorized ultra wideband commercial applications, but also for military applications which extend from 20 MHz up to multiple gigahertz.
As described in a patent application by John T. Apostolos and Roland A. Gilberg, entitled “Concatenated Vivaldi Notch/Meander Line Loaded Antennas” Ser. No. 10/629,500 filed on Jul. 29, 2003 and assigned to the assigned hereof and incorporated herein by reference, in order to decrease the low frequency cut-off of a Vivaldi notch meander line loaded antenna combination, the combined Vivaldi notch/meander line loaded antennas are concatenated, in one embodiment, by placing antennas side by side and electrically connecting them through the utilization of a common side plate. As a result, one side plate is shared by two adjacent antennas. What is accomplished by the concatenation is to in essence double the size of the antenna at the lower frequencies. Depending on how many side-by-side antennas are concatenated, the size of the overall array may be tripled or quadrupled. Another way to expand the size is to arrange a pair of concatenated antennas on top of another pair of concatenated antennas in a quad configuration. Here the bottom plates of the upper pair are shared and form the top plates of the bottom pair. With this quad configuration, the size is four times that of a single combined Vivaldi notch/meander line loaded antenna. The reason that they can be considered four times the size is that they are all directly connected together, which is accomplished by using the meander lines themselves to make the connections.
What has been found is that at the low frequency end, assuming that one has two antennas which are concatenated, then these two elements act like one element so as to effectively lower the low frequency cut-off of the pair. As one goes higher in frequency, one transitions to a region in which these concatenated antenna elements act like separate elements. This has a particularly beneficial result because at higher frequencies, beam forming can be made to occur. Note that at the higher frequencies, one does not need larger element size since the low frequency cut-off is not an issue. The result that is at the higher frequencies, each of the elements operates independently, and since one doesn't need the extra volume to go lower at the higher frequencies, one gets the usual benefits of an array of antenna elements. While the elements themselves may be capable of a 30:1 bandwidth spread, if wants to go to a 100:1 bandwidth spread by decreasing low frequency cut-off, then one has to combine four elements. The combination of two elements results in a 50 or 60:1 spread, whereas the combination of two more elements permits the 100:1 spread due to the increased size of the overall antenna acting as a single antenna at the lower frequencies.
The result in the lower frequencies is that in one embodiment, one gets coverage down to as low as 20 MHz, whereas in the upper frequencies, one can steer the beam from the antenna elements since the antenna elements act independently. It will be appreciated that this antenna is scalable in frequency. One could scale the dimensions so as to move the operation of the antenna to different frequency bands.
Note that for a quad concatenation, one has twelve feed points. For horizontal polarization, six feed points are combined, whereas for vertical polarization, six other feed points are combined. For right hand circular polarization or left hand circular polarization, the outputs of the six-way combiners for the horizontal and vertical polarizations are utilized in a 90° hybrid combiner, the outputs of which are the right hand circular polarized and the left hand circular polarized signals.
It has been found that by the above concatenation, not only is the low frequency cut-off decreased, the single lobe characteristic of a single combined Vivaldi notch/meander line loaded antenna is preserved for the lower frequencies, and steerable beams are formable at the upper frequencies. Note, the concatenation of the individual Vivaldi notch/meander line loaded antennas results in overall gain.
It will be appreciated that at the low end of the band, one is feeding the concatenated elements basically in phase, so that at the low frequencies, the concatenated antenna elements operate as one large antenna. The result is that while one may be steering the wave at low frequencies in the same direction, the lobes are so wide it simply doesn't matter.
While the above-described Vivaldi notch antennas work exceedingly well, concatenating these antennas is mechanically difficult due to the split, gap or spacing between the horizontal plates and the vertical or side plates. As a result, egg crate-type multiple horn arrays of these elements are somewhat rickety and mechanically unstable without massive mounting hardware.